GB2267362A1 discloses an elevator installation having a plurality of elevators and a group controller. Each elevator comprises an elevator car which is moved by an elevator drive. During normal operation of the elevator installation, a landing call which is entered by a passenger on a call input landing is detected by the group controller, and is allocated to an elevator. The elevator car of the allocated elevator is moved by the elevator drive to the call input landing of the landing call, in order to allow the passenger to enter the elevator car. Once the passenger has entered the elevator car, he enters a car call for a destination landing in the elevator car, in response to which the elevator drive moves the elevator car to the destination landing. Furthermore, the group controller uses the landing calls and the car calls to estimate the traffic on each landing. The traffic estimation means an estimated amount of traffic to a destination landing, a presence or absence of demands on a landing, a waiting time on a landing, a departure time from a landing, a number of passengers who arrive on one landing or leave a landing, as well as the presence or absence of excessively long waiting times on one landing, or of excessively long departure times from one landing. If there is a large demand on one landing, the elevator installation is changed by the group controller to express operation, and one elevator is removed from the landing call allocation. The elevator car of the removed elevator is moved directly by the elevator drive to the landing with the high demand, in order that passengers can enter the elevator car. Once the passengers have entered the elevator car, the elevator car is moved directly by the elevator drive to a supposed destination landing. A check is then carried out to determine whether the high demand on that landing has or has not decreased. If yes, the group controller changes back from express operation to normal operation of the elevator installation, and the removed elevator is returned to the landing call allocation.